6250 XiI(C2Cl3)(PEtJ2
aCH3 x
Li
Ni(o-tolyl)(C2C1,)(PEt,)2
y
4
3
I
5
p
UCH3 + 3
h’i(o-C1C,H,) (CLC13)(PEt3)2
other functional group “handles,”* optically active samples can be readily obtained through the Andersen synthesis3 or uia asymmetric oxidation of thioethers. We herein report the first method, t o our knowledge, for the direct determination of optical purities of sulfoxides. In appropriate optically active solvents, the nmr spectra of enantiomeric type 1 sulfoxides are sufficiently different to allow not only direct determinations of enantiomeric purity, but also correlations of absolute configuration. H
I
HO-C-CF,
0-S-R
CH, ( R ) - l , R =alkyl, a r y l
?
yield of a compound believed to be 6, mp 155.5-156.5,’ which, on thermolysis in tetrachloroethylene or on treatment with bromine in hexane, afforded 7. Reaction of 6 with HCI in ether afforded small amounts of 3 and chlorobenzene. The above series of reactions suggests strongly that 3 is chloro( trichlorovinyl) bis( triethy1phosphine)nickel(II), presumably derived from oxidative addition of tetrachloroethylene t o a nickel(0) species generated in the decomposition of 1. The compound exists in the trans configuration suggested by the low dipole moment of 1.95 D and the general features of the Et3P proton resonances. In view of the evidence for the generation of benzyne via the thermal decomposition of benzenediazonium-2-carboxylate, the formation of 6 possibly results from “insertion” of benzyne into the nickel-chlorine bond of 3. The formation of o-trichlorovinylchlorobenzene from bromination of 6 appears t o be an example of a coupling reaction induced by oxidative addition of bromine to 6 and is probably related to the coupling reactions reported by Corey. Acknowledgments. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, and to the University of North Dakota grant-in-aid program for support of this research. (13) M . Stiles, R. G. Miller, and U. Burckhardt, J . A m . Chem. SOC., 85, 1792 (1963). (14) E. I. Corey and M. F. Semmelhack, ibid., 89, 2755 (1967). (15) NDEA Predoctoral Fellow, 1965-1968.
Roy G. Miller, Darryl R. Fahey,’j David P. Kuhlman Department of Chemistry, Utiicersiry of North Dakota G r a d Fork$, North Dakota 58201 Receiced July 3, I968
Optically Active Solvents in Nuclear Magnetic Resonance Spectroscopy. VII. Direct Determination of Optical Purities and Correlations of Absolute Configurations of Sulfoxides’ Sir: While dissimilarly substituted sulfoxides, asymmetric by virtue of the tetrahedral configuration a t sulfur, have not been resolved except through the agency of (1) For part VI, see W. H. Pirkle, T. G. Burlingame, and S . D. Beare, Tetrahedron Lett., in press.
Journal of the American Chemical Society
1
90:22
8 ‘ O*s-CH,
1
0 menthyl
(-)4R 1-2
(-)-(R)-3
For example, in achiral solvents, the 100-MHz nmr spectrum of partially resolved methyl t-butyl sulfoxide, prepared5 by the action of t-butylmagnesium chloride on a 1.78: 1.00 mixture6 of the two diastereomeric (-)-menthyl methanesulfinates (3),’ shows two sharp singlets in a 3 : l ratio, However, in (-)-(R)-2,2,2trifluorophenylethano18 (2), the methyl and t-butyl resonances of the two sulfoxide enantiomers have appreciably different chemical shifts, and the spectrum of the partially resolved sulfoxide consists of two unequally intense t-butyl resonances (6 1.01 and 1.02, relative intensities 1.59 : 1.OO) and two unequally intense methyl resonances (6 2.09 and 2.07, relative intensities 1.63 : 1.OO). Since by virtue of fast-exchange processes, the optical purity of the solvent affects only the cheniical shift differences between the resonances of the enantiomers and not their relative intensities, this nmr method is, to our knowledge, the first method for the direct determination of the enantiomeric purity of a sulfoxide. It is well known that sulfoxides associate with alc o h o l ~ ,and ~ it seems reasonable t o assume that the spectral nonequivalence observed for enantiomers of unsymmetrical sulfoxides in optically active alcohol 2 (2) One possible exception is the resolution of ethyl p-tolyl sulfoxide with platinum complexes containing optically active a-methylbenzylamine: A. C. Cope and E. A. Caress, J . Amer. Chem. SOC., 88, 1711 (1966). (3) I
